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Wed, 09 Sep 2026 15:54:04 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (smtpav01.fra02v.mail.ibm.com [10.20.54.100]) by smtprelay06.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 689Fs2CM47513858 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 9 Sep 2026 15:54:02 GMT Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4D0B720043; Wed, 9 Sep 2026 15:54:02 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B2BBD20040; Wed, 9 Sep 2026 15:53:52 +0000 (GMT) Received: from [9.61.255.18] (unknown [9.61.255.18]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTPS; Wed, 9 Sep 2026 15:53:52 +0000 (GMT) Message-ID: <335b35d4-c8c9-4453-bf8e-0b1650d90f2e@linux.ibm.com> Date: Wed, 9 Sep 2026 21:23:48 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 03/22] coredump: set the minimum send buffer size To: Christian Brauner , linux-fsdevel@vger.kernel.org Cc: Jacob Lalonde , Josef Bacik , Jann Horn , Alexander Viro , Jan Kara , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Omar Sandoval , Jacob Lalonde , Shuah Khan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linuxppc-dev@lists.ozlabs.org References: <20260820-work-coredump-sparse-v2-0-ba32dd718c51@kernel.org> <20260820-work-coredump-sparse-v2-3-ba32dd718c51@kernel.org> Content-Language: en-US From: R Nageswara Sastry In-Reply-To: <20260820-work-coredump-sparse-v2-3-ba32dd718c51@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTA5MDE3MyBTYWx0ZWRfX111mlzSK7dLH AzIOnE1Oiswmd/ml1MHooNK96Jks8teAErxOPugWNBFt7WjdPiuz0rvE9EDYs31TKExlklp451T rncb17Te4eCGRINaSqj8T6Xqkv9S3h0= X-Proofpoint-ORIG-GUID: AnSIL4jHWFOgr-A1ayJ_vQa372N_SrpQ X-Authority-Analysis: v=2.4 cv=NMDlPU6g c=1 sm=1 tr=0 ts=6aa1811d cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=PjksA4QEkjs4iweiPkkA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTA5MDE3MyBTYWx0ZWRfX2ULqPz4mUGwj aUC17TmSMzwvp2OY65UMNDM0WI/7MGIAbm7QqwQKl6De4dymoQiBq7AHGZ6amm45djaAQoR1eZP VtTBgNYVRt1IkWdI040wCuzQjoAujK5Qtm+kLkbt2BHymBcidhiPAobf/d6lxq2UADZ7zmks7yA WjQJnK0PvCPna6rXENPblTVUHePD4aFZWxVT7I0RH8Sj7V28FPS1u1D7+UO91B+qo1zxOBC4srZ h/deht+Ex6D1sAvOaJkIliLRlfcLWKjP8QDWC+TB4t4/HicxcyU5EE5Q933crnIh9Cw54d0IQvR sakJIVOp1R1fi2BeH94gIyP0LErXdqaWPNxgh5+dwetNOejnF/0bgCSV5uUGL9j8vSa5HB7wQ9U sDFYWXTvK6I0RYWPleCjbmbXKRPfhLJlJc1uMzwcTwCx/U332d6o2kXxrdK3hdgLWwGc0GGJFmZ +mn6UaETfeRyYjPOz9Q== X-Proofpoint-GUID: iGDXdF9uRxGhfeKK4m4ZTFTZH1Hki_zQ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-08_03,2026-09-09_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 spamscore=0 lowpriorityscore=0 clxscore=1015 adultscore=0 impostorscore=0 bulkscore=0 malwarescore=0 priorityscore=1501 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609090173 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: B42F840004 X-Stat-Signature: qthxbwuricafasin15ac1gnn8ruaqcix X-Rspam-User: X-HE-Tag: 1788969253-338902 X-HE-Meta: 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 qr3coi3s t/s+lFaYX+hWZWKatwGvXbL04dytQ9dDyCngBDBqrcYXE75YHBsPbWBNSwOGLJ7HrMuGjSA5qKIMfPn59Bv20H7y6jw3EufDCTApO3V3/oFUb+a+Zrw2NwnYgm+VH4QVStyRAxB6Ms8fv9xEzTZu0K45g2RxzcWcqr1CQsxEpqKbCqSnXKOMDNyo1P84c9N5Vj+mU87vRDMNe0NIjfUurHkIbtUTomLqrt4cFFTjTCbGuZgMChghbodogkJto5dxSz2G3VYFvYcH2sOWlYmYl0Llsj9D7Yy6kHjvOjOJy79vBNstNu0oybR7X/iPTaWbGTSyA++jeFzvfOpAGBMUvRCCWLPGb+njBi0DvIpez/OKulfljOTX1uKaMAA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 20.08.2026 4:39 AM, Christian Brauner wrote: > The send buffer of the coredump socket is subject to the limit in > net.core.wmem_default. af_unix uses sk_sndbuf / 2 - 64 bytes for a > single skb. That means a send buffer below that would split a page-sized > write into multiple skbs. Raise the send buffer to leave room for a > page-sized write plus the header. The default value is well above that. > So we really change it when it's below our minimum. > > Signed-off-by: Christian Brauner (Amutable) Tested-by: R Nageswara Sastry System: ppc64le LPAR (IBM POWER), Linux 7.3-rc2 > --- > fs/coredump.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/fs/coredump.c b/fs/coredump.c > index ac4e922c9cb9..24a6405ea242 100644 > --- a/fs/coredump.c > +++ b/fs/coredump.c > @@ -665,6 +665,9 @@ static int umh_coredump_setup(struct subprocess_info *info, struct cred *new) > } > > #ifdef CONFIG_UNIX > +/* af_unix halves the send buffer to size a single skb. */ > +#define COREDUMP_SOCK_SNDBUF_MIN (3 * PAGE_SIZE) > + > static bool coredump_sock_connect(struct core_name *cn, struct coredump_params *cprm) > { > struct file *file __free(fput) = NULL; > @@ -690,6 +693,10 @@ static bool coredump_sock_connect(struct core_name *cn, struct coredump_params * > if (retval < 0) > return false; > > + /* Don't let a page-sized write split into several skbs. */ > + socket->sk->sk_sndbuf = max_t(int, socket->sk->sk_sndbuf, > + COREDUMP_SOCK_SNDBUF_MIN); > + > file = sock_alloc_file(socket, 0, NULL); > if (IS_ERR(file)) > return false; > -- Thanks and Regards R.Nageswara Sastry